1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus provided with a heater type fixing device.
2. Description of the Related Art
Modern image forming apparatuses, such as laser printers, are provided with a removable photoconductor unit. The photoconductor unit comprises a photoconductive drum, and besides, a main charger and a cleaning device surrounding the drum. Further, the unit has finger lugs which are provided individually near two axially opposite end portions of the drum. An operator can take out the photoconductor unit from the housing of the printer by pulling it up with his fingers hooked to the lugs. Arranged beside the photoconductive drum are an optical system for exposing the outer circumferential surface of the drum on the basis of print data and a developing device for supplying the drum with a toner.
A toner image is formed on the photoconductive drum through a series of operations of the main charger, exposure system, and developing device. This toner image is transferred, by the agency of a transfer charger, to the surface of a paper sheet which is delivered from a paper feeder to the transfer charger. Thereafter, the paper sheet, having the toner image thereon, is delivered to a heater-type fixing device, whereupon the toner image is fixed on the sheet.
Since the fixing device is a heating element, it is generally located adjacent to the lower-course side of the photoconductor unit, with respect to the feeding direction of the paper sheet, across a ventilation space, lest the individual components of the unit be heated to an excessively high temperature. The temperature of each component of the photoconductor unit, especially the cleaning device which adjoins the fixing device, is prevented from excessively increasing by means of air in the ventilation space, which forms a heat insulating layer. Thus, waste toner particles in the cleaning device are prevented from solidifying.
The fixing device comprises a heating roller heated to a predetermined temperature by means of a tubed heater or the like, a pressure roller pressed against the heating roller, and a cover which conceals at least the heating roller to keep it at the predetermined temperature. The fixing device further comprises a maintenance member for cleaning the heating roller.
When the paper sheet, having the toner image thereon, is delivered along a paper transportation path to the heating roller and the pressure roller, it is transported between these rollers. As this is done, the toner image on the paper sheet is fixed thereon by heat and pressure from these rollers.
According to the laser printer constructed in this manner, the operator's fingers or hand sometimes may touch the cover of the fixing device during inspection of the interior of the printer, removal of jammed paper, etc. In such a case, the top face of the cover is heated to a high temperature of about 80.degree. C. to 90.degree. C. by the heating roller, so that the operator may possibly suffer a burn. This involves a problem on safety.
Formed between the fixing device and the photoconductor unit, moreover, is the ventilation space in which fingers can be inserted. In some cases, therefore, the operator may erroneously remove the unit from the housing with his hands on the end portions of the unit on the sides of the fixing device and the photoconductive drum, without holding the lugs for the purpose. If this is done, the photoconductor unit cannot be held stably, and the drum may possibly be damaged by being unexpectedly brought into contact with the developing device, housing, etc. In this case, moreover, the operator's fingers touch the drum on which a photoconductive layer is formed, so that the photoconductive layer will be soiled by fingerprints or the like. If the drum is damaged or soiled, it is difficult to obtain high-quality prints.